This proposal is for HIV Vaccine Preparedness studies with the following aims: 1) assess the feasibility of a vaccine efficacy trial in NYC. 2) to determine the seroincidence of HIV and its association with behavioral and biological cofactors; 3) to validate risk assessment scales to measure risk behavior associated with HIV transmission: 4) to evaluate the antigenic and genetic variability of HIV in the study population; 5) to contribute specimens for subsequent genetic and immunologic analysis.